Low profile fusion cage and insertion set

ABSTRACT

A bone fusion implant includes a rigid body having a distal end, a proximal end and a longitudinal axis extending between the distal and proximal ends and a concave channel formed in the body between the distal and proximal ends, the concave channel being formed about an axis extending in a direction substantially perpendicular to the longitudinal axis of the body. The body has a first rigid cylindrical outer wall extending between the distal end of the body and the concave channel and a second rigid cylindrical outer wall extending between the proximal end of the body and the concave channel. The body also has a first opening at the distal end, a second opening at the proximal end and a hollow, internal chamber extending between the first and second openings.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to and claims priority from U.S.Provisional Application No. 60/128,113, filed Apr. 7, 1999.

BACKGROUND

1. Field of the Invention

The present application relates to a low profile fusion cage and aninsertion set for the low profile fusion cage.

2. Background of the Invention

2. Known spinal implants, such as those used for vertebral fusion, areoften used in pairs to provide adequate, evenly distributed support andfusion inducement. Because of limited space for implantation and forsurgical maneuvering, it is sometimes difficult or unfeasible toimplement a pair of implants that otherwise have desirable dimensionsand attributes. Certain existing implant designs are configured forclose, adjacent placement to other implants, but none achieve optimumperformance, versatility or ease of insertion.

SUMMARY

Summary of the Invention

It is an object of the present invention to provide an implant design,and associated instruments and methods, that provide optimumconfigurations for placement of adjacent implants in close proximitywith optimum performance. These objects and others are achieved throughthe present invention implant configuration and associated instrumentsand method.

In a preferred embodiment, a fusion implant according to the presentinvention is provided with a concave cut-away portion on acircumferential surface of an elongated implant. The concave portionaccommodates the outer contour of an adjacently placed implant having acorresponding concave surface. A novel dual tang distractor tool isprovided with two over-lapping cross-sectional configurations tofacilitate close insertion and placement of implants according to thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present disclosure are described hereinwith reference to the drawings wherein:

FIG. 1 is a perspective view of the fusion cage of the presentdisclosure;

FIG. 2 is a side view of the fusion cage of FIG. 1;

FIG. 3a is a cross-sectional view of the fusion cage taken along linesB—B of FIG. 1;

FIG. 3b is a cross-sectional view of the fusion cage as shown in FIG.3a, with a conventional implant cage of similar view placed adjacentlythereto.

FIG. 4 is a perspective view of the tang retractor of the presentdisclosure;

FIG. 5 is a perspective view of the guide of the present disclosure;

FIG. 6 is a perspective view illustrating attachment of the guide to thetang retractor;

FIG. 7 is a perspective view of the plate of the impactor;

FIG. 8 is a front, perspective view of an alternative embodiment of thepresent invention; and

FIG. 9 is a front, perspective view of another alternative embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-3a illustrate perspective, side and end views of the low profilefusion cage (10) of the present invention. The present invention cage(10) is of the type known commercially as the Ray TFC™ Fusion Cagecurrently marketed by Surgical Dynamics, Inc. The Ray TFC™ Fusion Cageis disclosed in commonly assigned U.S. Pat. No. 4,961,740, the contentsof which are incorporated herein by reference.

The fusion cage (10) disclosed herein can be implemented with anotherfusion cage to reduce the total amount of space occupied by twoconventional fusion cages placed side by side. The fusion cage (10) hasa helical thread (14) for facilitating insertion and securing of thecage (10) in a vertebral disc space. The thread (14) is carved out toform concave portions (16, 17) to reduce the profile of the thread. Asshown, the concave portions (16, 17) are preferably provided 180 degreesapart. If desired, only one concave portion is necessary to carry outthe present invention. It is possible, also, to provide more than twoconcave portions if desired. The concave portions (16, 17) allow two ormore cages (10, 11) to be placed close together as the radiused portionof one cage (11) is placed within the concave portion (17) of anadjacent cage (10), as shown in FIG. 3b. As can be appreciated, thecombined width (transverse space) of the two low profile cages (10, 11)placed in this fashion is less than the combined width if twoconventional cages without at least one of them having a concave portionwere placed side by side.

FIGS. 4-7b illustrate an insertion instrument set for fusion cagesaccording to the present invention. The instrument set includes a tangretractor (20), a guide (30) and an impactor (40) and impactor plate(41). The tang retractor (20) includes a pair of spaced apart tangs (21)which are dimensioned and configured as wedges at the distal end forinsertion into and distraction of the disc space. The configuration ofthe tangs (21) and the manner in which they distract the disc space isdescribed in pending U.S. patent application Ser. No. 08/889,661, filedJul. 8, 1997, the contents of which are incorporated herein byreference.

The tang retractor (20) includes a pair of proximally extending slottedtabs (22) for mounting the tabs (42) of the impactor plate (41) when theimpactor plate (41) is mounted to the proximal end of the distractor(20). The tabs (42) are inserted into the slots (23) of the tabs (22) tomount the impactor plate (41) and the elongated integral impactor (40),which is connected to the impactor plate (41) by threads (43, 45), tothe tang retractor (20). The impactor (40) can then be impacted ortapped at its proximal end (47) by a suitable tool, such as a hammer, toinsert the tang (21) into a vertebral space. After insertion, the tabs(42) are slid out of engagement with slots (23) to separate and removethe impactor (40) and impactor plate (41), leaving the tang retractor(20) in place with the tangs (21) inserted in the vertebral space.

The guide (30) is then attached to tang retractor (20) by inserting thedistal end pin (32) into the longitudinal slot (25) of the retractor(20). The distal end pin (32) is seated within the slot (25) so that theguide (30) can be pivoted, about the pin (32), with respect to the fixedtang retractor (20) between alignment with each of the two openings (26,27) of the tang retractor (20), respectively. Each of the openings (26,27) is configured to receive a fusion cage along with a conventionalcage insertion tool (not shown). The guide (30) is rotated about pin(32) so that its axial bore (34) is aligned with one of the openings(26, 27) of the tang retractor (20) during hole preparation through arespective one of the openings. Suitable tools, such as those describedin the aforementioned application Serial No. 08/889,661, are insertedthrough the bore (34) to prepare the space for fusion cage insertion.Fusion cages such as the type of the present invention, are theninserted via an elongated insertion tool through the bore (34) and therespective tang retractor opening (26, 27) for placement within thevertebral space. Each cage is placed so that one of the concave portions(16, 17) faces the adjacent opening or bore in the vertebral space. Theguide (30) is subsequently rotated so that axial bore (34) is alignedwith the other opening (26, 27) in the retractor 20. Another fusioncage, either with or without concave portions, is inserted in a similarmanner as described above so that its outer circumferential portion fitswithin the concave portion (16, 17) of the first-inserted fusion cage.

It is contemplated that an interlocking device (33) be provided toretain the guide (30) in each of its two aligned positions relative tothe tang retractor (20) during site preparation and insertion of afusion cage therethrough.

Alternate embodiments of the present invention, such as those shown inFIGS. 8-9, include variously configured implant bodies having a concaveportion to facilitate close, adjacent placement with additional implantbodies. For instance, the implant body (100) in FIG. 8 is a half-ovalhaving a central opening (102) to facilitate bone fusion, and a concaveside wall (104) configured to matingly receive a circumferential, convexwall (106) of an adjacent, oval implant (108). The implant body (200) ofFIG. 9, is generally cylindrical and has a concave channel (202) alignedgenerally perpendicularly to a longitudinal axis running between openends (204, 206).

It can be appreciated that the tang retractor (20) having a lengthapproximately equal to its width increases visibility as well as enablesthe user to more easily remove extraneous disc tissue because of theincreased mobility of instruments, e.g. rongeurs, inserted through theretractor 20. While this is the preferred embodiment, the length of theretractor (20) may be varied as desired to achieve different advantages.

While the preferred embodiment has been disclosed herein, it isunderstood and contemplated that modifications and variations may beemployed without departing from the scope of the present invention.

What is claimed is:
 1. A bone fusion implant comprising: a rigid bodyhaving a distal end, a proximal end and a longitudinal axis extendingbetween said distal and proximal ends; a concave channel formed in saidbody between said distal and proximal ends, said concave channel beingformed about an axis extending in a direction substantiallyperpendicular to said longitudinal axis of said body; said body having afirst rigid cylindrical outer wall extending between said distal end ofsaid body and said concave channel; and said body having a second rigidcylindrical outer wall extending between said proximal end of said bodyand said concave channel, wherein said body has a first opening at saiddistal end, a second opening at said proximal end and a hollow, internalchamber extending between said first and second openings.
 2. The implantas claimed in claim 1, wherein said first and second openings are incommunication with said hollow, internal chamber.
 3. The implant asclaimed in claim 1, further comprising one or more bone growth inducingsubstances disposed in said hollow, internal chamber.
 4. The implant asclaimed in claim 1, wherein said concave channel has a cross-sectionaldimension that is less than a cross-sectional dimension of said firstrigid cylindrical outer wall of said body.
 5. The implant as claimed inclaim 4, wherein said cross-sectional dimension of said concave channelis less than a cross-sectional dimension of said second generallycylindrical outer wall of said body.
 6. The implant as claimed in claim1, wherein said body includes external threads adapted to facilitateinsertion of said body between opposing vertebrae.
 7. A bone fusionimplant comprising: a rigid body made of metal having a distal end, aproximal end and a longitudinal axis extending between said distal andproximal ends; a concave channel formed in said body between said distaland proximal ends, said concave channel being formed about an axisending in a direction substantially perpendicular to said longitudinalaxis of said body; said body having a first rigid cylindrical outer wallextending between said distal end of said body and said concave channel;and said body having a second rigid cylindrical outer wall extendingbetween said proximal end of said body and said concave channel, whereinsaid body has a first opening at said distal end, a second opening atsaid proximal end and a hollow, internal chamber extending between saidfirst and second openings.